System for detecting a touch gesture of a user, device comprising the system, and method

ABSTRACT

System for detecting a touch gesture of a user on a detection surface, comprising: a processing unit; and an accelerometer to detect a vibration at the detection surface and generate a vibration signal. The processing unit is configured to: acquire the vibration signal, detect, in the vibration signal, a signal characteristic which can be correlated to the touch gesture of the user, detect, in the vibration signal, a stationarity condition preceding and/or following the detected signal characteristic, and validate the touch gesture in the event that both the signal characteristic and the stationarity condition have been detected. An electrostatic charge sensor may also be used as a further parameter to validate the touch gesture.

BACKGROUND Technical Field

The present disclosure relates to a system for detecting a touch gestureof a user, a device comprising the detection system, and a method fordetecting a touch gesture of a user.

Description of the Related Art

Nowadays, one of the most important causes of malfunction of mobiledevices, in particular cell phones, relates to mechanical buttons, whichare subject to breakage due to structural weakness, use of fragileflexible PCBs, problems of water resistance, etc.

The solutions to mechanical buttons provide buttons based on capacitivesensors, particularly suitable for implementation on full-screendevices; however they are not always reliable as they are subject todisturbances resulting from the presence of environmental electricalcharge.

BRIEF SUMMARY

According to the present disclosure, a system for detecting a touchgesture of a user, a device comprising the detection system, and amethod for detecting a touch gesture of a user are provided.

In an embodiment, the system for detecting a touch gesture of a user ona detection surface comprises:

-   -   a processing unit;    -   an accelerometer, operatively coupled to the processing unit,        configured to detect a vibration at said detection surface and        generate a corresponding vibration signal, wherein the        processing unit is configured to: acquire the vibration signal,        detect, in the vibration signal, a signal characteristic which        can be correlated to said touch gesture of the user, detect, in        the vibration signal, a stationarity condition preceding and/or        following said detected signal characteristic, and validate said        touch gesture by the user in the event that both the signal        characteristic and the stationarity condition preceding and/or        following said signal characteristic have been detected.

Furthermore, in an embodiment, the operation of detecting said signalcharacteristic comprises: calculating a filtered vibration signal byfiltering, through a high-pass filter, the vibration signal; detecting afirst peak of the filtered vibration signal exceeding a first threshold;and detecting a second peak of the filtered vibration signal exceeding asecond threshold, wherein the first threshold is one of a positivethreshold and a negative threshold, and the second threshold is theother of said positive threshold and said negative threshold.

Furthermore, in an embodiment, the processing unit is further configuredto sample the vibration signal, and the operation of calculating thefiltered vibration signal is carried out using a digital filter, saidoperation of detecting the first peak comprising: detecting a firstsample of the filtered vibration signal which exceeds the firstthreshold; detecting a second sample of the filtered vibration signalimmediately preceding the first sample and having a value, in modulus,which is lower than the value, in modulus, of the first sample; anddetecting a third sample of the filtered vibration signal immediatelyfollowing the first sample and having a value, in modulus, which islower than the value, in modulus, of the first sample, said first peakcorresponding to the first sample.

Furthermore, in an embodiment, said operation of detecting the secondpeak comprises: detecting a fourth sample of the filtered vibrationsignal which exceeds the second threshold; detecting a fifth sample ofthe filtered vibration signal immediately preceding the fourth sampleand having a value, in modulus, which is lower than the value, inmodulus, of the fourth sample; and detecting a sixth sample of thefiltered vibration signal immediately following the fourth sample andhaving a value, in modulus, which is lower than the value, in modulus,of the fourth sample, said second peak corresponding to the fourthsample.

Furthermore, in an embodiment, the operation of detecting said signalcharacteristic further comprises verifying that the first peak and thesecond peak are at a mutual distance, in terms of number of samplescomprised between the first peak and the second peak, which is lowerthan a maximum value of number of samples.

Furthermore, in an embodiment, the operation of detecting, in thevibration signal, a stationarity condition preceding said signalcharacteristic comprises: after detecting the first peak, verifying thatthe values of a first plurality of samples of the filtered vibrationsignal preceding the first peak are comprised in a first range ofreference values.

Furthermore, in an embodiment, the operation of detecting, in thevibration signal, a stationarity condition following said signalcharacteristic comprises: after detecting the second peak, verifyingthat the values of a second plurality of samples of the filteredvibration signal following the second peak are comprised in a secondrange of reference values.

Furthermore, in an embodiment, the operation of detecting, in thevibration signal, a stationarity condition following said signalcharacteristic further comprises discarding a third plurality of samplesof the filtered vibration signal immediately following the second peakand comprised between the second peak and said second plurality ofsamples of the filtered vibration signal.

Furthermore, in an embodiment, the system further comprises anelectrostatic charge variation sensor, operatively coupled to theprocessing unit, configured to detect an electrostatic charge variationat said detection surface and, as a result, generate a charge variationsignal.

Furthermore, in an embodiment, the processing unit is further configuredto generate a variance signal by calculating the variance of the chargevariation signal.

Furthermore, in an embodiment, the processing unit is further configuredto detect a maximum point of the variance signal when said signalcharacteristic which can be correlated to said touch gesture of the useris detected in the vibration signal.

Furthermore, in an embodiment, the processing unit is further configuredto: verify whether the maximum point of the variance signal is in apredefined relationship with a third threshold, and in the event thatboth the signal characteristic and the stationarity condition precedingand/or following said signal characteristic have been detected, validatesaid touch gesture only if the maximum point of the variance signalmeets said predefined relationship with the third threshold.

Furthermore, in an embodiment, the processing unit is further configuredto: in the event that both the signal characteristic and thestationarity condition preceding and/or following said signalcharacteristic have been detected, and if the maximum point of thevariance signal meets said predefined relationship with the thirdthreshold, verify whether the variance signal is in a stationaritycondition and validate said touch gesture only if the variance signalmeets said stationarity condition.

Furthermore, in an embodiment, the stationarity condition of thevariance signal is met if at least one current sample of the variancesignal has a value comprised within a range of stationarity referencevalues.

Furthermore, an embodiment provides the step of detecting a touch eventthat persists over time if the variance signal remains above a fourththreshold for a time which is longer than a predefined touch time.

The present disclosure also relates to a method for detecting a touchgesture of a user on a detection surface, using a system whichcomprises: a processing unit; and an accelerometer, operatively coupledto the processing unit, configured to detect a vibration at saiddetection surface and generate a corresponding vibration signal, themethod comprising the steps, carried out by the processing unit, of:acquiring the vibration signal, detecting, in the vibration signal, asignal characteristic which can be correlated to said touch gesture ofthe user, detecting, in the vibration signal, a stationarity conditionpreceding and/or following said detected signal characteristic, andvalidating said touch gesture by the user in the event that both thesignal characteristic and the stationarity condition preceding and/orfollowing said signal characteristic have been detected.

Furthermore, in an embodiment, the step of detecting said signalcharacteristic comprises: calculating a filtered vibration signal byfiltering, through a high-pass filter, the vibration signal; detecting afirst peak of the filtered vibration signal exceeding a first threshold;and detecting a second peak of the filtered vibration signal exceeding asecond threshold, wherein the first threshold is one of a positivethreshold and a negative threshold, and the second threshold is theother of said positive threshold and said negative threshold.

Furthermore, in an embodiment, the method comprises the step of samplingthe vibration signal, and wherein the step of calculating the filteredvibration signal is carried out using a digital filter, said step ofdetecting the first peak comprising: detecting a first sample of thefiltered vibration signal that exceeds the first threshold; detecting asecond sample of the filtered vibration signal immediately preceding thefirst sample and having a value, in modulus, which is lower than thevalue, in modulus, of the first sample; and detecting a third sample ofthe filtered vibration signal immediately following the first sample andhaving a value, in modulus, which is lower than the value, in modulus,of the first sample, said first peak being chosen corresponding to thefirst sample.

Furthermore, in an embodiment, the step of detecting the second peakcomprises: detecting a fourth sample of the filtered vibration signalthat exceeds the second threshold; detecting a fifth sample of thefiltered vibration signal immediately preceding the fourth sample andhaving a value, in modulus, which is lower than the value, in modulus,of the fourth sample; and detecting a sixth sample of the filteredvibration signal immediately following the fourth sample and having avalue, in modulus, which is lower than the value, in modulus, of thefourth sample, said second peak being chosen corresponding to the fourthsample.

Furthermore, in an embodiment, the step of detecting said signalcharacteristic further comprises verifying that the first peak and thesecond peak are at a mutual distance, in terms of number of samplescomprised between the first peak and the second peak, which is lowerthan a maximum value of number of samples.

Furthermore, in an embodiment, the step of detecting, in the vibrationsignal, a stationarity condition preceding said signal characteristiccomprises: after detecting the first peak, verifying that the values ofa first plurality of samples of the filtered vibration signal precedingthe first peak are comprised in a first range of reference values.

Furthermore, in an embodiment, the step of detecting, in the vibrationsignal, a stationarity condition following said signal characteristiccomprises: after detecting the second peak, verifying that the values ofa second plurality of samples of the filtered vibration signal followingthe second peak (p2) are comprised in a second range of referencevalues.

Furthermore, in an embodiment, the step of detecting, in the vibrationsignal, a stationarity condition following said signal characteristicfurther comprises discarding a third plurality of samples of thefiltered vibration signal immediately following the second peak andcomprised between the second peak and said second plurality of samplesof the filtered vibration signal.

Furthermore, in an embodiment, wherein said system further comprises anelectrostatic charge variation sensor, operatively coupled to theprocessing unit, the method further comprising the steps of detecting,through the electrostatic charge variation sensor, an electrostaticcharge variation at said detection surface and generating as a result,through the electrostatic charge variation sensor, a charge variationsignal.

Furthermore, in an embodiment, the method further comprises the step ofgenerating a variance signal by calculating the variance of the chargevariation signal.

Furthermore, in an embodiment, the method further comprises the step ofdetecting a maximum point of the variance signal when said signalcharacteristic which can be correlated to said touch gesture of the useris detected in the vibration signal.

Furthermore, in an embodiment, the method further comprises: verifyingwhether the maximum point of the signal of (S_(Q_var)) is in apredefined relationship with a third threshold, and in the event thatboth the signal characteristic and the stationarity condition precedingand/or following said signal characteristic have been detected,validating said touch gesture only if the maximum point of the variancesignal meets said predefined relationship with the third threshold.

Furthermore, in an embodiment, the method further comprises: in theevent that both the signal characteristic and the stationarity conditionpreceding and/or following said signal characteristic have beendetected, and if the maximum point of the variance signal meets saidpredefined relationship with the third threshold, verifying whether thevariance signal is in a stationarity condition and validating said touchgesture only if the variance signal meets said stationarity condition.

Furthermore, in an embodiment, the stationarity condition of thevariance signal is met if at least one current sample of the variancesignal has a value comprised within a range of stationarity referencevalues.

Furthermore, in an embodiment, the method further comprises the step ofdetecting a touch event that persists over time if the variance signalremains above a fourth threshold for a time which is longer than apredefined touch time.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the disclosure, embodiments thereof arenow described, purely by way of non-limiting example and with referenceto the attached drawings, wherein:

FIG. 1A illustrates a vibrational signal generated by an accelerometerfollowing a movement;

FIG. 1B illustrates the signal of FIG. 1 a after a filtering step with ahigh-pass filter, according to the prior art;

FIG. 2 illustrates a further signal generated by an accelerometer,filtered with the filter described with reference to FIG. 1B, wherein atouch event by a user is identified on the basis of the exceedance ofpredefined thresholds, according to the prior art;

FIG. 3 schematically illustrates an electronic or electromechanicalsystem or chip or package, according to an aspect of the presentdisclosure;

FIG. 4 illustrates a method for detecting a touch gesture exploiting avibratory signal of an accelerometer, according to an aspect of thepresent disclosure;

FIGS. 5-7 graphically illustrate respective steps of the method of FIG.4 ;

FIG. 8 illustrates the electronic or electromechanical system or chip orpackage of FIG. 3 further comprising an electrostatic charge sensor,according to a further aspect of the present disclosure;

FIG. 9 illustrates an embodiment of an electrostatic charge sensor,which can be used in the system of FIG. 8 ;

FIG. 10 illustrates a method for detecting a touch gesture exploiting avibratory signal of an accelerometer and an electrostatic chargevariation signal of the sensor of FIG. 9 , according to an aspect of thepresent disclosure;

FIGS. 11 and 12 graphically illustrate respective steps of the method ofFIG. 10 ;

FIG. 13 graphically illustrates an electrostatic charge variation signalgenerated by a touch prolonged over time of a detection electrode of theelectrostatic charge sensor of FIG. 9 ; and

FIG. 14 illustrates an electronic device including the electronic orelectromechanical system or chip or package of FIG. 3 or FIG. 8 .

DETAILED DESCRIPTION

MEMS accelerometers are used to implement electronic buttons, as theyare suitable for detecting movements resulted from the touch, or “tap,”(or double tap) of the user, exploiting suitable algorithms that detectand process the acceleration data provided by these MEMS accelerometers.Even this solution, however, is subject to environmental or useconditions that may cause a false touch detection (for example due toaccelerations resulting from movements of the user's body which aresimilar to a touch even if they are not such).

In some devices that do not suffer from battery consumption in stand-by(for example because they have a large battery), it is possible to usethe touch-screen technology to detect the touch gesture. This type ofsolution ensures high accuracy, but the implementation cost is high and,as said, requires a non-negligible energy consumption.

In an embodiment known to the Applicant, the touch gesture is identifiedby processing and monitoring an acceleration signal or vibratory signal,provided by an accelerometer following a touch gesture, filtered througha high-pass filter. The high-pass filter is, in particular, configuredto filter the low frequency signal components (e.g., acceleration due togravity, movements attributable to human activity) and leave the highfrequency signal components, including the signal componentsattributable to touch, unaltered. By way of non-limiting example, thehigh frequency components of interest for the present disclosure arehigher than 50 Hz.

The filtering is, in particular, obtained through a digital “Slope”filter. Therefore, with reference to FIGS. 1A and 1B, the raw signalprovided by the accelerometer (in FIG. 1A, the signal S_(acc_raw)) issampled (i.e., converted into digital); again in FIG. 1A, the n-thsample at time t_(n) is identified as acc(t_(n)) and the sampleimmediately preceding time t_(n-1) is identified as acc(t_(n-1)).

FIG. 1B illustrates the signal of FIG. 1A filtered through the Slopefilter (filtered signal S_(acc_filt)). The n-th filtered sample isobtained according to the following formula:

acc_filt(t _(n))=[acc(t _(n))−acc(t _(n-1))]/2

By setting a suitable threshold on the filtered signal, it is possibleto identify possible touch events at the local exceedance of thisthreshold, by at least one sample of the filtered signal. The thresholdmay be of a fixed type (preset and/or configurable) or of adaptive type.

FIG. 2 shows, by way of example, a further accelerometric signal,filtered with the Slope filter according to what has been described withreference to FIG. 1B. FIG. 2 also shows two thresholds (one positive +Thand one negative −Th). In FIG. 2 , the exceedance of the threshold +Thoccurs by two samples acc_filt(t₁) and acc_filt(t₁₁) in two respectivetime instants t₁ and t₁₁ and causes the generation of an interrupt eventthat identifies the occurred touch at the times t₂ and t₁₂ since thesignal returns within the range defined by the thresholds −Th and +Th bya predefined time.

This technical solution has the advantage of requiring low energyconsumption and low cost; furthermore, it allows to obtain high accuracyin the identification of any touch event, but at the same time generatesa significant number of false positives, for example in cases whereinthe accelerometer detects vibrations resulting from an unwanted touch inproximity to the device (for example on the strap of a smartwatch, andin other similar situations).

The problems mentioned hereinabove are overcome by the solutions thatprovide the use of a touch sensor, which however, as said, has a highcost and significant energy consumption. Furthermore, the touch sensortechnology is not applicable to any device (for example to earphones)due to the size and/or current consumption required for implementing atouch sensor.

The need is therefore felt to overcome the drawbacks of the prior art byproviding a system for detecting a touch gesture of a user, a devicecomprising the detection system, and a method for detecting a touchgesture of a user which are enhanced.

FIG. 3 illustrates, with the reference number 1, an electronic orelectromechanical system or chip or package, according to an aspect ofthe present disclosure. Hereinafter, this system or chip or package 1will be referred to as “electronic system” without thereby losinggenerality. The electronic system 1 comprises, e.g., integrates oraccommodates in a case, a processing unit 2 and an MEMS motion sensor,e.g., an accelerometer 4, which is operatively coupled to the processingunit 2.

The accelerometer 4 is configured to detect at least one accelerationcomponent along an acceleration axis orthogonal to a detection surface(see for example, in FIG. 14 , the surface 102). The detection surfaceis a surface at which a user causes a vibration by touching this surfacewith, for example, his/her finger (touch event or touch). For example,the accelerometer 4 is of triaxial type, configured to detectacceleration components along three axes X, Y, Z orthogonal to eachother; for detecting the touch, it is possible to choose the Z axis asthe only detection axis, or otherwise choose any combination of two ormore axes, possibly attributing a greater weight to one of them.

It is noted that the electronic system 1 (and therefore theaccelerometer 4) may be installed or used with any orientation withrespect to the Earth's gravitational axis, and therefore theaccelerometer 4 may be oriented in such a way as not to have thevertical detection axis (Z axis) necessarily in the direction of theforce of gravity. Therefore, the detection axis of the force impressedby the touch may be chosen orthogonal to the sensor itself or along theassumed direction of the touch (on the basis of the modes in which theelectronic system 1 is installed or operates or is expected to operate);this also allows any unwanted impulses, which would come from otherdirections, to be filtered out.

As an alternative or addition to the above, it is also possible, in afurther embodiment, to consider a suitable vector composition of thethree detection axes of the accelerometer 4, to maximize the signal inthe direction of the impressed force.

The processing unit 2 receives an acceleration signal, or vibrationsignal, S_(acc_raw) (raw signal) from the accelerometer 4 and generates,according to the acceleration signal S_(acc_raw), a touch detectionsignal I_(S) (e.g., an interrupt signal) by a user.

The accelerometer 4 is for example an integrated sensor of semiconductormaterial, made using MEMS technology, of a per se known type and therebynot described in detail.

The processing unit 2 is for example a microcontroller or an MLC(Machine Learning Core) residing in the ASIC (Application SpecificIntegrated Circuit) integrated in the MEMS, or a microprocessor of othertype.

The electronic system 1 may be a stand-alone system or be part, forexample, of a printed circuit, or even be part of a more complex deviceor system. In fact, it is possible to provide a device or system thatintegrates a combo of sensors, and therefore in addition to the threeaxes X, Y, Z of the accelerometer 4, there may also exist dedicatedchannels for other detections (e.g., gyroscope, temperature sensor,etc.).

FIG. 4 illustrates, through a flow chart, steps of a method fordetecting the touch implemented by the electronic system 1, inparticular by the processing unit 2, according to an aspect of thepresent disclosure.

With reference to step 40, the processing unit 2 receives and acquires,from the accelerometer 4, the raw signal S_(acc_raw) generated by theaccelerometer 4, for example the signal S_(acc_raw) of FIG. 1A. Then,step 42, the processing unit 2 carries out an operation of filtering theraw signal S_(acc_raw) through a high-pass filter; in particular, thefiltering operation is carried out through the Slope filter describedwith reference to FIG. 1B, obtaining the filtered signal S_(acc_filt).The filtered signal S_(acc_filt) is for example the signal of FIG. 1B,or FIG. 2 , or FIG. 5 (or FIG. 6 , or FIG. 7 wherein filtered signalsresulting from events other than the touch event are illustrated).

Then, step 44, a detection of a first peak p1 (positive or negative) iscarried out in the filtered signal and, subsequently, a detection of asecond peak p2 which is an inverted peak (negative or positive,respectively) is carried out. In this regard see FIG. 5 , wherein thepeak p1 corresponds to a sample of the filtered signal S_(acc_fat) thatexceeds the negative threshold −Th, and therefore is hereinafterreferred to as the “negative peak”, whereas the peak p2, following p1,corresponds to a sample of the filtered signal S_(acc_filt) that exceedsthe positive threshold +Th, and therefore is hereinafter referred to asthe “positive peak”.

In an embodiment of the present disclosure, the negative peak p1 isidentified as a sample that exceeds the threshold −Th and which isimmediately preceded and followed by respective samples p1′ and p1″which have a value, in modulus, which is lower than the value, inmodulus, of the negative peak p1. Similarly, the positive peak p2 isidentified as a sample that exceeds the threshold +Th and which isimmediately preceded and followed by respective samples p2′ and p2″which have a value, in modulus, which is lower than the value, inmodulus, of the positive peak p2. It is noted that, in this example, thesamples p1″ and p2′ coincide.

It is apparent that the conditions expressed hereinabove may bemodified, for example by requiring a plurality of samples that precedeand/or follow the positive p2 or negative peak p1 and having respectivevalues which are lower in modulus than the value reached by the peak p1or p2.

In an embodiment, the number of samples between the negative peak p1 andthe positive peak p2 (in the example of FIG. 5 , there is only onesample p1″/p2′) is lower than a predefined maximum number, to betterdiscriminate a “touch” event from an event of other type. For example,this number of samples is equal to 2 (sampling the raw signalS_(acc_raw) at 400 Hz) or to multiples of 2 (sampling the raw signalS_(acc_raw) at multiples of 400 Hz). Other values may be chosen asneeded.

Returning to FIG. 4 , a stationarity condition of the filtered signalS_(acc_filt) preceding the first peak p1 is detected in step 46. Inparticular, this step aims to detect whether the first peak detected iscaused by an actual touch event or is caused by a more complex “shock”event, such as for example a shaking situation of the electronic system1 that accommodates the accelerometer 4. In fact, in the case ofshaking, there is a continuous perturbation of the signal of theaccelerometer 4, which may also result in the generation of one or morepeaks that exceed the preset thresholds ±Th, such as for exampleillustrated in FIG. 6 .

Step 46 is described herein with graphic reference to FIG. 6 , forimproved clarity. In FIG. 6 the same notation of FIG. 5 is used toidentify the first peak (p1) and the inverted peak (p2) that exceed thepreset thresholds ±Th. To discriminate between touch events and eventsof other type, such as for example shaking, according to an aspect ofthe present disclosure, a history buffer is used wherein a plurality ofsamples p_pre (temporally) preceding the first peak p1 are stored. Inparticular, this plurality of samples is a number equal to or greaterthan 8 (for example, 16 or 32), and includes the sample p1′ and theother samples immediately preceding the sample p1′. When the first peakp1 is detected (according to what has been previously discussed), thehistory buffer is analyzed, according to step 46, to verify astationarity condition of the samples stored therein. In particular, thestationarity condition is verified if all the samples stored in thehistory buffer, or a subset thereof, are comprised between a positivethreshold +Th′ and a negative threshold −Th′ (with |+Th′|<|+Th| and|−Th′|<|−Th|). For example, the value in modulus of the thresholds ±Th′is comprised between 0.0625 g and 2 g.

In an embodiment, the stationarity condition is assessed on the samplespresent in the history buffer except for a subset of samples immediatelypreceding the first peak p1 (for example the 2 samples immediatelypreceding the first peak p1). The Applicant has in fact verified thatthe signal relating to the touch includes the samples immediatelypreceding the peak.

In step 48 the second peak p2 (inverted peak) is sought and, if any,detected, according to what has already been previously discussed.

In step 50 a stationarity condition of the filtered signal S_(acc_filt)following the second peak p2 is detected. In particular, this step aimsto detect whether the second peak p2 detected is caused by an actualtouch event or is caused by a more complex “shock” event, such as forexample a clapping situation, which persists for a certain period oftime, and which causes the generation of an accelerometric signalwherein a series of positive and negative above-threshold peaks (similarto the sequence of the first peak p1 and the second peak p2) arefollowed by a plurality of further peaks or a high noise signal, as forexample illustrated in FIG. 7 (wherein the same notation of FIG. 5 isused to identify the first peak p1 and the inverted peak p2).

Therefore, in order to identify this situation, as said generated forexample by clapping hands, according to an aspect of the presentdisclosure, a plurality of samples following the second peak p2 areanalyzed.

In particular, this plurality of samples is a number equal to or greaterthan 8 (for example, 16 or 32), and includes the sample p2″ and othersamples immediately following the sample p2.″ In particular, thestationarity condition is verified if all the samples immediatelyfollowing the second peak p2, or a subset thereof, are comprised betweena positive threshold +Th″ and a negative threshold −Th″ (with|+Th″|<|+Th| and |−Th″|<|−Th|). For example, the value in modulus of thethresholds ±Th″ is comprised between 0.0625 g and 2 g.

In an embodiment, the stationarity condition is assessed on a pluralityof samples p_post following the second peak p2 except for a subset ofsamples p_excl immediately following the second peak p2 (e.g., excludingthe 6-8 samples immediately following the second peak p2). In fact, theApplicant has verified that in some practical conditions, in the eventof a signal resulting from a “touch” (therefore the event to bedetected), after the second peak p2 a step is observed wherein theoscillation of the signal of the accelerometer 4 persists for a limitedtime, similarly to a “rebound” effect. In this manner, the stationaritycondition is assessed by excluding this settling step following thesecond peak p2.

The method described with reference to FIG. 4 may be modified as needed.In particular, the first peak may indifferently be a negative orpositive peak and, as a result, the second peak (inverted peak) is apositive or negative peak respectively. Furthermore, the stationarityverifications of steps 46 and 50 may be carried out both or one as analternative to the other. For example, it is possible to provide forcarrying out only the stationarity verification of step 46 and not thestationarity verification of step 50, or vice versa.

Furthermore, the method of FIG. 4 may also be used to identify amultiple touch event (e.g., double or triple touch), verifying thepresence of a plurality of consecutive touch events in a predefined (andpossibly configurable) period of time. To this end, it is possible touse a timer or counter usable to, after the occurrence of a touch event,count the number of samples that are present before the following touchevent. If this number of samples is comprised in a predefined range (orlower than a maximum value) then the second touch event is correlatedwith the first touch event to validate the multiple touch event.

In an embodiment of the present disclosure, illustrated in FIG. 8 , theelectronic system 1 comprises (e.g., integrates or accommodates in thecase), in addition to the elements illustrated in FIG. 1 and previouslydescribed, also an electrostatic charge variation sensor 6 operativelycoupled to the processing unit 2.

FIG. 9 illustrates, by way of non-limiting example, an embodiment of theelectrostatic charge variation sensor 6. The electrostatic chargevariation sensor 6 comprises an input electrode 8, coupeable to a bodyportion of a user. In particular, the electrostatic charge variationsensor 6 of FIG. 9 is configured to be placed in electrical orelectrostatic contact with a body portion of a user, for detecting thetouch. Typically, the user uses his/her finger, and in particularhis/her fingertip, to perform the touch.

The input electrode 8 forms part of a differential input 9 of aninstrumentation amplifier 12.

An input capacitor C_(I), biased through a direct current (DC) generatorG_(I) and an input resistor R_(I) connected in parallel with each otherand with the input capacitor C_(I) are at the ends of the differentialinput 9. In use, the voltage Vd across the input capacitor C_(I) remainsconstant until the user touches the electrode 8; in this case, thevoltage across the input capacitor C_(I) varies due to the electriccharge/discharge process through the user's body. In presence of a touchevent and consequently after a transient (the duration thereof beingdefined by the constant RC of the parallel between capacitor C_(I) andresistor R_(I)) the voltage Vd returns to its steady state value.

The instrumentation amplifier 12 is essentially formed by twooperational amplifiers OP1 and OP2. A biasing stage (buffer) OP3 is usedto bias the instrumentation amplifier 12 to a common mode voltageV_(CM).

The inverting terminals of the operational amplifiers OP1 and OP2 areconnected to each other through a resistor R₂. Since the two inputs ofeach operational amplifier OP1, OP2 are to be at the same potential, theinput voltage Vd is also applied across R₂ and causes, through thisresistor R₂, a current equal to I₂=Vd/R₂. This current I₂ does not comefrom the input terminals of the operational amplifiers OP1, OP2 andtherefore flows through the two resistors R₁ connected between theoutputs of the operational amplifiers OP1, OP2, in series with theresistor R₂; the current I₂, thus flowing through the series of thethree resistors R₁-R₂-R₁, produces an output voltage Vd′ given byVd′=I₂·(2R₁+R₂)=Vd·(1+2R₁/R₂). Therefore, the overall gain of thecircuit of FIG. 9 is Ad=(1+2R₁/R₂). The differential gain depends on thevalue of the resistor R₂ and may therefore be modified by acting on theresistor R₂.

The components of the amplifier 12 are chosen in such a way that theamplifier 12 has high impedance (of the order of 10⁹ Ohm) in itspassband (chosen between DC and 500 Hz).

The voltage Vd across the input capacitor C_(I) is detected by theamplifier 12.

The differential output Vd′ is therefore proportional to the potentialVd at input, and is provided at input to an analog-to-digital converter14, which provides the charge variation signal S_(Q) for the processingunit 2 at output. The charge variation signal S_(Q) is, for example, ahigh-resolution digital stream (16 bits or 24 bits).

According to an embodiment, the analog-to-digital converter 14 isoptional, since the processing unit 2 may be configured to work directlyon the analog signal, or may itself comprise an analog-to-digitalconverter for converting the signal Vd′.

According to an embodiment, having an analog-to-digital converter (ADC)with suitable characteristics (e.g., differential input, high inputimpedance, high resolution, dynamic range optimized for the quantitiesto be measured, low noise) the amplifier stage 12 may be omitted, byfeeding the signal directly to the input of the analog-to-digitalconverter.

FIG. 10 illustrates, through a flow chart, the operations carried out bythe processing unit 2 to process the signal provided by theelectrostatic charge variation sensor 6.

With reference to step 60, the processing unit 2 receives, from theelectrostatic charge variation sensor 6, the charge variation signalS_(Q). The signal S_(Q) is, in the described embodiment, a digitalsignal. FIG. 11 exemplarily illustrates the signal S_(Q) generatedfollowing an event of contact between the input electrode 8 and thefingertip of a user (touch event). The values of the potential Vd,induced by the physical contact of the user with the input electrode 8,are represented on the ordinate axis of the charge variation signalS_(Q). This value is here expressed in LSB (“Least Significant Bit”),that is the minimum digital value output from the analog-to-digitalconverter, which is proportional to the voltage detected at the inputelectrode 8. Typically 1 LSB corresponds to a value comprised between afew μV and a few tens of μV. The constant of proportionality (orsensitivity) depends on the gain of the amplifier, on the resolution ofthe analog-to-digital converter and on any digital processing (e.g.,oversampling, decimation, etc.). The LSB representation is common in theart and disregards a quantification in physical units, as the aim istypically to detect relative variations, with respect to a steady orbase state. The progressive numbers of the acquired sample arerepresented on the abscissa axis of the charge variation signal S_(Q).

Then, step 62, the processing unit 2 performs an operation ofcalculating or estimating the variance of the signal S_(Q), obtainingthe variance signal S_(Q_var). The calculation or estimation of thevariance is carried out in a per se known manner, for example asdescribed by Tony Finch in “Incremental calculation of weighted mean andvariance,” University of Cambridge Computing Service, February 2009.Other methods may be used, such as for example, approaches based on IIRfilters, or yet others.

FIG. 12 illustrates the variance signal S_(Q_var), and the filteredaccelerometer signal S_(acc_filt), superimposed to each other. It isnoted that FIG. 12 shows the square root of the signals S_(acc_filt) andS_(Q_var). The operation of calculating the square root of the variancevalue has the function of compressing the dynamics of the output signal,as well as of bringing it back to the initial physical dimension. Inother words, the variance squares, the square root restores the physicaldimensions. For example, if the physical dimension x of the input signalis [x]²; after the variance it is [(x²)]²; after the square rootoperation it returns to [x]².

Then, step 64, a step of searching for a maximum point of the signalS_(Q) is carried out. The maximum point corresponds, in this examplewherein digital signals (samples) are used, to the sample whose value(on the ordinate axis) is the greatest with respect to a plurality ofcomparison samples. In particular, each sample is compared with themaximum value detected up to that instant and, if it is greater than themaximum value, the maximum value is updated to the value of the currentsample. This operation is initiated (e.g., the maximum is reset to thecurrent value) after the detection of a “shock” event by theaccelerometer 4. The shock event considered is any event that causes thegeneration of a signal of the accelerometer 4 which, after having beenfiltered as previously described (e.g., high-pass filter or Slopefilter), exceeds the threshold +Th (positive exceedance) or −Th(negative exceedance). The exceedance of the threshold ±Th is confirmedif at least one sample of the signal S_(acc_filt) exceeds the threshold±Th.

In FIG. 12 , it is the sample #28 of the signal S_(acc_filt) thatnegatively exceeds the threshold −Th (first peak p1). This eventtriggers the search for the maximum of the signal S_(Q_var). At sample#28, the maximum value is reset to the current value of the signalS_(Q_var). Therefore, from the corresponding sample #28 (or from thesubsequent, the sample #29) of the signal S_(Q_var), it is assessedwhether this sample has a value (here, in LSB) which is greater than themaximum value calculated up to that instant. This operation continuesuntil the detection of an actual touch signal, as described hereinafterin the following step 66. The maximum value assumed by the S_(Q_var) issaved in memory. In the example of FIG. 12 , the sample having themaximum value was found at the sample #36 of the signal S_(Q_var)(sample p_(MAX)).

Then, step 66, the confirmation of the occurred touch is awaited on thebasis of the signal of the accelerometer 4 (e.g., the interrupt signalI_(S) previously mentioned). In FIG. 12 , this signal is generated atsample #90.The search for the maximum value of the signal S_(Q_var)discussed in step 64 is thus interrupted.

In this embodiment, the final decision of the occurred touch is taken,as well as a function of the signal of the accelerometer 4, also as afunction of the signal acquired by the electrostatic charge variationsensor 6 and processed as previously discussed. In particular, uponreceiving the interrupt signal I_(s), a current sample of the signalS_(Q_var) is acquired (for the purposes of the present disclosure, thiscurrent sample is exemplarily the one at which the interrupt wasreceived). The value of the current sample is compared to a thresholdTh_Q.

In an embodiment, if the value of the sample p_(max) of the signalS_(Q_var) is in a predefined relationship with this threshold (inparticular, it exceeds the threshold Th_Q) the touch event is confirmedand one or more functionalities correlated to this touch event (notobject of the present disclosure) are activated. The threshold Th_Q ispreset to a value chosen during the design step and in any casechangeable (e.g., comprised between 8000 and 12000 LSB); this value ischosen on the basis of the sensor and electrode used, through laboratorytests.

In a further embodiment, if the value of the sample p_(max) of thesignal S_(Q_var) is in said predefined relationship with this threshold(in particular, it exceeds the threshold Th_Q), then a furthercomparison of the value of the current sample of the signal S_(Q_var)with a second threshold Th_Q′ chosen as a fraction of the maximum valueof the previously identified signal S_(Q_var) (i.e., in this example,that found at the sample #36) is carried out. For example, the secondthreshold Th_Q′ is equal to ¼ of the maximum value of the signal S_(Q)var. In this embodiment, the aforementioned operations are carried outon the variance signal under square root (as previously said). Otherembodiments are however possible. If both comparisons with thethresholds Th_Q and Th_Q′ comply with a respective predefined condition(in particular, the value of the sample p_(MAX) of the signal S_(Q_var)exceeds the threshold Th_Q and the current value of the signal S_(Q_var)is lower than the threshold Th_Q′), then the touch event is confirmedand one or more functionalities correlated to this touch event (notobject of the present disclosure) are activated.

In a further embodiment, additional or alternative to those previouslydescribed, the use of the signal resulting from the electrostatic chargesensor 6 may also be used to detect a touch condition that persists overtime, for example when the user performs the touch while holding thepressure for a continuous time of a few tenths of a second (e.g., 0.6seconds). This event, herein identified as a “long touch,” may be usedto activate further or different functionalities with respect to thosethat may be activated with a traditional, typically rapid, touch event.

The long touch event is identified if the signal S_(Q_var) remains abovethe threshold Th_Q for a time which is longer than a minimum time,predefined during the design step and in any case configurable asneeded. It is apparent that the comparison threshold for the long touchmay be a further threshold different from the thresholds Th_Q, forexample chosen equal to 10000 LSB. FIG. 13 illustrates an example ofsignal S_(Q_var) that identifies a long touch.

Furthermore, the method of FIG. 10 may also be used to identify amultiple-touch event (e.g., double or triple touch), verifying thepresence of a plurality of consecutive touch events in a predefined (andpossibly configurable) period of time, similarly to what has beendescribed hereinabove with reference to the method of FIG. 4 .

FIG. 14 schematically illustrates an electronic device 100 whichincludes the previously described electronic system 1, according to anyof the embodiments of the present disclosure.

For example, the electronic device 100 comprises a touch-sensitivesurface 102 (detection surface), which is the surface at which the userperforms the physical touch gesture. This surface is, for example, ofplastic material, with a thickness of approximately 1 mm. The electronicsystem 1 is placed below the surface 102, for example accommodated in anown package.

In order to optimize the generation of both signals S_(Q) and S_(acc),it is preferable, but not necessary, that the relative arrangementbetween the surface 102 and the electronic system 1 meets one or more ofthe following parameters:

-   -   the sensors for detecting the acceleration and the charge        variation are arranged as proximate as possible to the area        identified as the touch surface; and    -   the sensors for detecting the acceleration and the charge        variation are placed proximate to each other, to optimize the        correlation of the respective signals.

The disclosure may be effectively implemented in all those deviceswherein a mechanical contact cannot be present, or for impermeability,immunity to dust or mechanical strength requirements. Some examples:smartphones, smartwatches, True Wireless Stereos (TWS), headsets,appliances, industrial equipment, etc.

The advantages achieved by the present disclosure are apparent from theprevious description.

In particular, the use of an accelerometer and, in the respectiveembodiment, of an electrostatic charge sensor allow the consumptions tobe significantly reduced with respect to solutions that provide a sensorwith a panel of “touch-screen” type.

Furthermore, the solution described with reference to FIG. 4 (detectionof the stationarity before and/or after the detection of the first andsecond peaks) allows false positives to be significantly reduced. Thesolution that provides the use of the electrostatic charge sensorfurther improves the performances of rejections of false positives withrespect to the solution with accelerometer only.

Furthermore, the use of the electrostatic charge sensor expands therange of gestures that the user may use to give commands to the system100 (e.g., the long touch).

Variations and modifications may be applied to the present disclosure,without departing from the scope identified by the claims.

For example, respective operations of filtering (for example usinglow-pass or high-pass filters) the signals S_(acc) and S_(Q) may beprovided. In particular, the filtering has the function of removingnoise or non-significant frequency disturbing components, or lowfrequency components (e.g., gravity acceleration component or movementsattributable to human activity for S_(acc)), from the signals S_(acc)and S_(Q).

Furthermore, the processing of the signals of the accelerometer 4 and ofthe electrostatic charge sensor 6 may be implemented entirely inhardware, entirely in software or in mixed hardware/software form, asneeded.

A system (1) for detecting a touch gesture of a user on a detectionsurface (102), the system may be summarized as including a processingunit (2); an accelerometer (4), operatively coupled to the processingunit (2), configured to detect a vibration at said detection surface(102) and generate a corresponding vibration signal (S_(acc_raw)),wherein the processing unit (2) is configured to acquire the vibrationsignal (S_(acc_raw)), detect, in the vibration signal (S_(acc_raw),S_(acc_filt)), a signal characteristic (p1, p2) which can be correlatedto said touch gesture of the user, detect, in the vibration signal(S_(acc_raw), S_(acc_filt)), a stationarity condition preceding and/orfollowing said detected signal characteristic, and validate said touchgesture by the user in the event that both the signal characteristic andthe stationary condition preceding and/or following said signalcharacteristic have been detected.

The operation of detecting said signal characteristic (p1, p2) mayinclude calculating a filtered vibration signal (S_(acc_filt)) byfiltering, through a high-pass filter, the vibration signal(S_(acc_raw)); detecting a first peak (p1) of the filtered vibrationsignal (S_(acc_filt)) exceeding a first threshold (−Th; +Th); anddetecting a second peak (p2) of the filtered vibration signal(S_(acc_filt)) exceeding a second threshold (+Th; −Th), wherein thefirst threshold may be one of a positive threshold and a negativethreshold, and the second threshold may be the other of said positivethreshold and said negative threshold.

The processing unit (2) may be further configured to sample thevibration signal (S_(acc_raw)), and the operation of calculating thefiltered vibration signal (S_(acc_filt)) may be carried out using adigital filter, said operation of detecting the first peak may includedetecting a first sample (p1) of the filtered vibration signal(S_(acc_filt)) which exceeds the first threshold; detecting a secondsample (p1′) of the filtered vibration signal (S_(acc_filt)) immediatelypreceding the first sample (p1) and having a value, in modulus, whichmay be lower than the value, in modulus, of the first sample (p1); anddetecting a third sample (p1″) of the filtered vibration signal(S_(acc_filt)) immediately following the first sample (p1) and having avalue, in modulus, which may be lower than the value, in modulus, of thefirst sample (p1), said first peak corresponding to the first sample(p1).

Said operation of detecting the second peak (p2) may include detecting afourth sample (p2) of the filtered vibration signal (S_(acc_filt)) whichexceeds the second threshold; detecting a fifth sample (p2′) of thefiltered vibration signal (S_(acc_filt)) immediately preceding thefourth sample (p2) and having a value, in modulus, which may be lowerthan the value, in modulus, of the fourth sample (p2); and detecting asixth sample (p2″) of the filtered vibration signal (S_(acc_filt))immediately following the fourth sample (p2) and having a value, inmodulus, which may be lower than the value, in modulus, of the fourthsample (p2), said second peak corresponding to the fourth sample (p2).

The operation of detecting said signal characteristic (p1, p2) mayfurther include verifying that the first peak (p1) and the second peak(p2) may be at a mutual distance, in terms of number of samples includedbetween the first peak (p1) and the second peak (p2), which may be lowerthan a maximum value of number of samples.

The operation of detecting, in the vibration signal (S_(acc_raw),S_(acc_filt)), a stationarity condition preceding said signalcharacteristic (p1, p2) may include after detecting the first peak (p1),verifying that the values of a first plurality of samples (p_pre) of thefiltered vibration signal (S_(acc_filt)) preceding the first peak (p1)may be included in a first range of reference values (±Th′).

The operation of detecting, in the vibration signal (S_(acc_raw),S_(acc_filt)), a stationarity condition following said signalcharacteristic (p1, p2) may include after detecting the second peak(p2), verifying that the values of a second plurality of samples(p_post) of the filtered vibration signal (S_(acc_filt)) following thesecond peak (p2) may be included in a second range of reference values(±Th″).

The operation of detecting, in the vibration signal (S_(acc_raw),S_(acc_filt)), a stationarity condition following said signalcharacteristic (p1, p2) may further include discarding a third pluralityof samples (p_excl) of the filtered vibration signal (S_(acc_filt))immediately following the second peak (p2) and may be included betweenthe second peak (p2) and said second plurality of samples of thefiltered vibration signal (S_(acc_filt)).

The system may further include an electrostatic charge variation sensor(6), operatively coupled to the processing unit (2), configured todetect an electrostatic charge variation at said detection surface and,as a result, generate a charge variation signal (S_(Q)).

The processing unit (2) may be further configured to generate a variancesignal (S_(Q_var)) by calculating the variance of the charge variationsignal (S_(Q)).

The processing unit (2) may be further configured to detect a maximumpoint (p_(MAX)) of the variance signal (S_(Q_var)) when said signalcharacteristic which can be correlated to said touch gesture of the usermay be detected in the vibration signal (S_(acc_raw), S_(acc_filt)).

The processing unit (2) may be further configured to verify whether themaximum point (p_(MAX)) of the variance signal (S_(Q_var)) may be in apredefined relationship with a third threshold, and in the event thatboth the signal characteristic and the stationarity condition precedingand/or following said signal characteristic have been detected, validatesaid touch gesture only if the maximum point (p_(MAX)) of the variancesignal (S_(Q_var)) meets said predefined relationship with the thirdthreshold.

The processing unit (2) may be further configured to in the event thatboth the signal characteristic and the stationarity condition precedingand/or following said signal characteristic have been detected, and ifthe maximum point (p_(MAX)) of the variance signal (S_(Q_var)) meetssaid predefined relationship with the third threshold, verify whetherthe variance signal (S_(Q_var)) may be in a stationarity condition andvalidate said touch gesture only if the variance signal (S_(Q_var))meets said stationarity condition.

The stationarity condition of the variance signal (S_(Q_var)) may be metif at least one current sample of the variance signal (S_(Q_var)) has avalue included within a range of stationarity reference values.

The system may further include the step of detecting a touch event thatpersists over time if the variance signal (S_(Q_var)) remains above afourth threshold for a time which may be longer than a predefined touchtime.

An electronic device (100) may be summarized as including a detectionsurface (102) of a touch gesture by a user; and a system (1) fordetecting a touch gesture according to any of claims 1-15.

A method for detecting a touch gesture of a user on a detection surface(102), using a system (1) that may be summarized as including aprocessing unit (2); and an accelerometer (4), operatively coupled tothe processing unit (2), configured to detect a vibration at saiddetection surface (102) and generate a corresponding vibration signal(S_(acc_raw)), the method including the steps, carried out by theprocessing unit (2), of acquiring the vibration signal (S_(acc_raw)),detecting, in the vibration signal (S_(acc_raw), S_(acc_filt)), a signalcharacteristic (p1, p2) which can be correlated to said touch gesture ofthe user, detecting, in the vibration signal (S_(acc_raw),S_(acc_filt)), a stationarity condition preceding and/or following saiddetected signal characteristic, and validate said touch gesture by theuser in the event that both the signal characteristic and the stationarycondition preceding and/or following said signal characteristic havebeen detected.

Said system (1) may further include an electrostatic charge variationsensor (6), operatively coupled to the processing unit (2), the methodmay further include the steps of detecting, through the electrostaticcharge variation sensor (6), an electrostatic charge variation at saiddetection surface and generating as a result, through the electrostaticcharge variation sensor (6), a charge variation signal (S_(Q)).

The various embodiments described above can be combined to providefurther embodiments. Aspects of the embodiments can be modified, ifnecessary to employ concepts of the various embodiments to provide yetfurther embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A system, comprising: an accelerometer, configured to detect a touchgesture vibration at a detection surface and generate a vibration signalin response to the vibration; and a processing unit, coupled to theaccelerometer, the processing unit configured to: detect a signalcharacteristic of the touch gesture vibration; detect a stationaritycondition adjacent to the signal characteristic in a time sequence; andvalidate a touch gesture in response to the signal characteristic andthe stationary condition.
 2. The system of claim 1 wherein theprocessing unit is configured to: acquire the vibration signal; detect,in the vibration signal, the signal characteristic correlated to thetouch gesture; detect, in the vibration signal, the stationaritycondition adjacent to the signal characteristic in the time sequence. 3.The system according to claim 2, wherein the processing unit isconfigured to: calculate a filtered vibration signal with a high-passfilter and the vibration signal; detect a first peak of the filteredvibration signal exceeding a first threshold; and detect a second peakof the filtered vibration signal exceeding a second threshold.
 4. Thesystem according to claim 3, wherein the high-pass filter is a digitalfilter and the processing unit is configures to: detect a first sampleof the filtered vibration signal which exceeds the first threshold;detect a second sample of the filtered vibration signal immediatelypreceding the first sample and having a value in modulus lower than thevalue in modulus of the first sample; and detect a third sample of thefiltered vibration signal immediately following the first sample andhaving a value in modulus lower than the value in modulus of the firstsample, the first peak corresponds to the first sample.
 5. A method,comprising: detecting a touch gesture of a user on a detection surface;generating a vibration signal in response to a vibration at thedetection surface with an accelerometer; detecting a signalcharacteristic with a processing unit, the signal characteristiccorresponding to the touch gesture; detecting a stationarity conditionwith the processing unit, the stationary condition being adjacent to thesignal characteristic in a time sequence; and validating the touchgesture in response to the signal characteristic and the stationarycondition.
 6. The method of claim 5, comprising detecting, by anelectrostatic charge variation sensor operatively coupled to theprocessing unit, an electrostatic charge variation at said detectionsurface.
 7. The method of claim 6, comprising generating as a result ofthe detecting the electrostatic charge variation, by the electrostaticcharge variation sensor, a charge variation signal.
 8. A method,comprising: detecting a touch gesture on a detection surface by:generating a vibration signal with an accelerometer; detecting a signalcharacteristic from the vibration signal with a processing unit, thesignal characteristic being related to the touch gesture, the detectingthe signal characteristic including: generating a filtered vibrationsignal from the vibration signal; detecting a first peak of the filteredvibration signal exceeding a first threshold; and detecting a secondpeak of the filtered vibration signal exceeding a second threshold. 9.The method of claim 8, comprising: detecting a first sample of thefiltered vibration signal which exceeds the first threshold; anddetecting a second sample of the filtered vibration signal immediatelypreceding the first sample and having a value in modulus lower than thevalue in modulus of the first sample.
 10. The method of claim 9,comprising detecting a third sample of the filtered vibration signalimmediately following the first sample and having a value in moduluslower than the value in modulus of the first sample, the first peakcorresponds to the first sample.
 11. The method of claim 10, comprising:detecting a fourth sample of the filtered vibration signal which exceedsthe second threshold; and detecting a fifth sample of the filteredvibration signal immediately preceding the fourth sample and having avalue in modulus lower than the value in modulus of the fourth sample.12. The method of claim 11, comprising detecting a sixth sample of thefiltered vibration signal immediately following the fourth sample andhaving a value in modulus lower than the value in modulus of the fourthsample, the second peak corresponds to the fourth sample.
 13. The methodof claim 12, comprising verifying that the first peak and the secondpeak are at a mutual distance, in terms of number of samples between thefirst peak and the second peak, which is lower than a maximum value ofnumber of samples.
 14. The method of claim 13, comprising afterdetecting the first peak, verifying that values of a first plurality ofsamples of the filtered vibration signal preceding the first peak are ina first range of reference values.
 15. The method of claim 14,comprising after detecting the second peak, verifying that values of asecond plurality of samples of the filtered vibration signal followingthe second peak are in a second range of reference values.
 16. Themethod of claim 15, comprising discarding a third plurality of samplesof the filtered vibration signal immediately following the second peakand between the second peak and said second plurality of samples of thefiltered vibration signal.
 17. The method of claim 16, comprisingverifying whether the maximum point of the variance signal meets arelationship with a third threshold, and in response to detecting boththe signal characteristic and the stationarity condition adjacent to thesignal characteristic, validating the touch gesture only if the maximumpoint of the variance signal meets the relationship with the thirdthreshold.
 18. The method of claim 17, comprising detecting a touchevent that persists over time in response to the variance signal remainsabove a fourth threshold for a time which is longer than a predefinedtouch time.